In Mason 2, components have to write $self-> a lot to refer to attributes that were simple scalars in Mason 1. This eases the transition pain. $. was chosen because of its similar use in Perl 6.

This plugin falls under the heading of gratuitous source filtering, which the author generally agrees is Evil. That said, this is a very limited filter, and seems unlikely to break any legitimate Perl syntax other than use of the $. special variable (input line number).